Semiconductor devices are used for integrated circuits in a variety of electrical and electronic applications, such as computers, cellular telephones, radios, and televisions. One particular type of semiconductor device is a semiconductor storage device, such as a random access memory (RAM) device. Many RAM devices include many storage cells arranged in a two-dimensional array with two sets of select lines, word lines and bit lines. An individual storage cell is selected by activating its word line and its bit line. RAM devices are considered “random access” because any memory cell in an array can be accessed directly if the row and column that intersect at that cell are known.
A commonly used form of RAM is known as a dynamic RAM (DRAM) device. Dynamic random access memory has memory cells with a paired transistor and capacitor, wherein the capacitor requires periodic refreshing. One particular type of DRAM device is a synchronous DRAM (SDRAM) device, in which the memory cells are accessed synchronously. Synchronous dynamic random access memory often takes advantage of the burst mode concept to greatly improve performance by staying on the row containing the requested bit and moving rapidly through the columns. To achieve a high-speed operation, a double data rate (DDR) architecture is often used, during which two data transfers are made per clock cycle, one upon the rising edge of the clock and the other upon the falling edge.
As portable electronic devices become smaller, less expensive, and more power efficient, however, there has been an increased demand for low power and compact electronic systems in which DRAM is commonly used. Consequently, systems and methods are needed to reduce the size, power and cost of memory systems.